78 lines
4.5 KiB
HTML
78 lines
4.5 KiB
HTML
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="ODBC APIs: General concepts" />
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<meta name="abstract" content="The following general concepts apply to ODBC APIs:" />
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<meta name="description" content="The following general concepts apply to ODBC APIs:" />
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<title>ODBC APIs: General concepts</title>
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</head>
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<body id="odbcenvconnstate"><a name="odbcenvconnstate"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">ODBC APIs: General concepts</h1>
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<div><p>The following general concepts apply to ODBC APIs: </p>
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<dl><dt class="dlterm">Environments:</dt>
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<dd>The environment in which Windows<sup>®</sup> makes available some memory
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for ODBC to monitor its run-time information. </dd>
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<dt class="dlterm">Connections:</dt>
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<dd>Within the environment there can be multiple connections, each to a data
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source. The connections may be to different physical servers, to the same
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server, or any combination of both.</dd>
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<dt class="dlterm">Statements:</dt>
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<dd>Multiple statements can be run within each connection.</dd>
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<dt class="dlterm">Handles:</dt>
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<dd>Handles are identifiers for storage areas that are allocated by the Driver
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Manager or individual drivers. The three types of handles are: <dl><dt class="dlterm">Environment handle:</dt>
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<dd>Global information, that includes other handles. One handle is allowed
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per application.</dd>
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<dt class="dlterm">Connection handle:</dt>
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<dd>Information about connection to a data source. Multiple connection handles
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are allowed per environment.</dd>
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<dt class="dlterm">Statement handle:</dt>
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<dd>Information about a particular SQL statement. Multiple statement handles
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are allowed per connection. Statement handles can be reused for other SQL
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statements and long as the statement state is valid.</dd>
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<dt class="dlterm">Descriptor handle:</dt>
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<dd>Information about explicit descriptors that are associated with the connection
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handle. The application creates these, and asks the driver to use them instead
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of the implicit descriptors associated with a statement handle.</dd>
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</dl>
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<p>Essentially, a <strong>handle</strong> can be considered as an identifier
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for a resource that is recognized by ODBC (an environment, connection or statement).
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ODBC provides an identifier (the handle) for this resource that you can use
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in your program. Exactly what ODBC stores in the handle (which is held as
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a long integer) is not relevant. Be careful not to change the value, and to
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assign unique names to the variables that hold the various handles.</p>
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<p>Some
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APIs set the handle (for example, <span class="apiname">SQLAllocEnv</span> or <span class="apiname">SQLAllocHandle</span> with
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SQL_HANDLE_ENV handle type), and you must pass in a reference, or pointer
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to the variable. Some APIs refer to a handle that previously was set (for
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example, <strong>SQLExecute</strong>), and you must pass in the variable by value.</p>
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</dd>
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</dl>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaikodbcapiinfo.htm" title="Identify the files required to build an ODBC application.">Files required to build an ODBC application</a></div>
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</div>
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</div>
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</body>
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</html> |